For those who are interested:
I did some quick tests on the RC oscillator frequency for AT90S1200’s:
I only had four chips left, but here are the results:
Chip 1: 2.882 usec (to toggle PORTB in a loop)
Chip 2: 2.780 usec
Chip 3: 2.800 usec
Chip 4: 3.877 usec
Yep, I couldn’t believe it either. So I checked them again and sure enough – results were consistent.
Then I checked further and found the date code on chips 1-3 to be 9947 (week 47 1999). The fourth chip was 9727!
So between chips within a batch expect at least a 3% variation (probably more) and if you’re timing critical – just like wallpaper and paint - don’t mix your batches!